Coating Breakdown Analysis of Steel Plates in Marine Structures Naval Architecture and Marine ...

125 Pages·2015·8.6 MB·English

by  Silvia Sousa

Coating Breakdown Analysis of Steel Plates in Marine
Structures
Sílvia Cristina Guerreiro de Sousa
Thesis to obtain the Master Degree in
Naval Architecture and Marine Engineering
Supervisor: Professor Doutor Yordan Garbatov
Examination Committee
Chairperson: Professor Doutor Carlos Guedes Soares
Supervisor: Professor Doutor Yordan Garbatov
Member of the Committee: Professor Doutor Ângelo Teixeira
July 2015

"Learnfromyesterday,livefortoday,hopefortomorrow.
Theimportantthingisnottostopquestioning."
AlbertEinstein
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Acknowledgments
TherearemanytowhomIowethedeepestgratitudetothecompletionofthisdissertation.
Firstandforemost,Iwishtoexpressmydeepestgratitudetomyadvisor,Prof. DoutorYordanGarbatov,
forhismotivation,availability,knowledgeandexceptionalguidancealongthedevelopmentofthisstudy.
Itwasapleasurelearningfromhimandworkingunderhissupervision.
To all my friends and colleagues throughout all the Naval Engineering journey, a heartfelt thanks, for
their friendship, companionship, help, mutual support and for sharing such remarkable moments with
me,duringthisyears. Allofthem,certainly,helpedmetoreachthismomentandtobewhoIamtoday.
ToMauro,akindlythankyoufortheunconditionalsupport,motivationandforhisavailabilitytohelpme
and to discuss my work with me. Thank you for being my solid anchor and for always believing in me,
evenwhenIdidn’t.
Last but not least, a very special thanks to my family, especially my parents, Cidália and José, and my
sisterSandraforallthesupport, patience, trustandsacrificesduringthisyears. Withoutthem, noneof
thiswouldbepossible.
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Resumo
Oobjetivodestadissertaçãoéestudarocolapsodorevestimentodechapasdeaçoemestruturasmarí-
timassujeitasacompressãouniaxialnoplano. Estetrabalhoémotivadopelanecessidadedemelhorar
osrevestimentosdemodoapreveniracorrosãomarítimadoaço. Édesenvolvidoevalidadoummod-
elo de elementos finitos em ANSYS. É estudado o comportamento de encurvadura da chapa de aço
revestida, com imperfeições iniciais e uma macro-delaminação na interface, baseado no problema de
valores próprios da encurvadura e na análise não-linear. A análise não-linear permite grandes deslo-
camentoseimporocontatoentreorevestimentoeaplaca. Acompressãonaplacaeasimperfeições
causadas pela má preparação da superfície e/ou má aplicação do revestimento leva à criação de ten-
sõesresiduaiseconsequentementeàencurvaduralocaldacamadaderevestimento. Comoaumento
do carregamento, a encurvadura aumenta atingindo o tamanho crítico onde o revestimento começa a
delaminar. Baseadonaformaexponencialdomodelodezonacoesivaéimplementadoumelementode
interfacecomespessurazerosimulandoaadesãoentreplacaerevestimento. Quandoatensãonestes
elementos excede o valor crítico, a tensão é redistribuída, resultando na deformação dos elementos e
consequenteseparação/delaminaçãoaolongodainterface. Éestudadaainfluênciadocomprimentode
delaminação,daespessuradorevestimento,daspropriedadesmecânicasedeinterfacenocomporta-
mentodeencurvaduraepós-encurvaduradorevestimentodaplacadeaço. Baseadonestesresultados,
écriadoumdiagramadeavaliaçãodefalhadorevestimentoparadiâmetrosdemacro-delaminações.
Palavras-chave:
Colapso do Revestimento, Método dos Elementos Finitos, Encurvadura, De-
laminação,ZonaCoesiva,DiagramadeAvaliaçãodeFalha
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Abstract
Theobjectiveofthisdissertationistostudythecoatingbreakdownofsteelplatesinmarinestructures,
subjected to uniaxial in-plane compression. This work is motivated by the necessity of improving the
coating protection systems, in order to prevent the marine steel corrosion. A finite element model is
developed in ANSYS and its validation is performed. The buckling behaviour of the coated steel plate,
withaninitialimperfectionandamacro-delaminationintheinterface,isstudiedbasedontheeigenvalue
buckling and nonlinear strength analysis. Nonlinear analyses allow to take into account large displace-
ments and impose contact constraints between coating and plate. The compressive loads acting on
the plate, in addition to the imperfections caused by the inadequate steel surface preparation and/or
poor coating application, leads to the residual stresses creation and consequently the local buckling of
the coating layer occurs. As the load increases the buckling region increases reaching the critical size,
whenthecoatinglayerstartstodelaminate. Basedontheexponentialformofthecohesivezonemodel,
azerothicknessinterfaceelement,tomodeltheadhesionbetweenplateandcoatinglayer,isemployed.
When the stress in these elements exceeds the critical value, the stress field is redistributed, resulting
intheelementsdeformationandseparation/delaminationacrosstheinterface. Theinfluenceofdelami-
nationlength,coatingthickness,mechanicalandinterfacepropertiesonthebucklingandpost-buckling
behaviour of the steel plate coating are studied. Based on these results, a coating failure assessment
diagramforthemacro-delaminationdiametersiscreated.
Keywords:
Coating Breakdown, Finite Element Method, Buckling, Delamination, Cohesive Zone,
FailureAssessmentDiagram
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